New DOE project to study aerosols and tropical rainfall

Professor Marcelo Chamecki receives Department of Energy (DOE) award to investigate the influences of aerosols on rainfall in the Amazonia region.

The Amazonia region is unique in the world as
it experiences the deepest atmospheric convection with important
teleconnections to other regions and parts of the Earth’s climate. It
also represents the largest emissions of hydrocarbon compounds that exhibit
minor seasonal patterns in response to the year-round growing season and high
temperatures. Chamecki is leading a team of scientists from the United States
(from Duke University, Montana State University, and State University of New York at
Albany) and Brazil (from several universities and research centers)
to investigate the life cycle of secondary aerosols in pristine and polluted
environments. Investigations span biological and atmospheric conditions
influencing hydrocarbon emissions and chemical reactions of aerosol precursors,
formation and transport of aerosols from near the ground surface to the cloud
layer. Influences of aerosols on cloud formation and rainfall amounts
will be investigated in areas dominated by pristine forested landscapes and
regions influenced by urban environments, downwind of the City of Manaus,
Amazonas, Brazil. Chamecki and his collaborators will use aerosol
spectrometers, cloud condensation nuclei counters (CCNs), and meteorological
instruments deployed on tethered balloons and flux towers to generate unique
data sets to verify whether the aerosols formed from the reactions of
hydrocarbon compounds emitted by the rainforest meaningfully
influence rainfall (see Figure below). Numerical model simulation studies will
also be carried out over the course of three years. Field studies
will be done during February – March and September – October 2014. The
team expects to integrate the results into the Brazilian Earth System Model and
several US Earth System Models.

This figure shows
physical and chemical pathways originated from the canopy and transported all
the way up to the cloud base, illustrating the chemical transformations of hydrocarbons
to generate secondary organic aerosols (SOA). The proposed project seeks to
understand how such processes can influence cloud formation and rainfall
processes. Due to the chemical attributes of aerosols, clouds over rural
environments develop smaller cloud droplets undergoing inefficient coalescence
and collision, which could suppress rainfall, whereas clouds formed over
regions under urban influences develop larger droplets undergoing efficient
coalescence and collision, which could enhance rainfall.